Open thermal convection dolomitization: an example from East Yunnan (China)

• Published in: Geological magazine Vol. 158; no. 2; pp. 330 - 348
• Main Authors: Zhang, Jing-Qi, Jin, Zhen-Kui, Zhu, Xiao-Er, Li, Yang, Guo, Qi-Heng, Shi, Shu-Ting
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.02.2021
• Subjects: Asia; carbonate rocks; carbonatization; Cellular convection; chemical composition; China; Computational fluid dynamics; Convection; Distribution; Dolomitization; Dolostone; Far East; Fault lines; Fluid flow; fluid inclusions; Fluids; Free convection; Geology; Geophysics; Global positioning systems; GPS; Heat flux; Heat transfer; Hydrocarbons; igneous and metamorphic rocks; inclusions; isotopes; Liangshan Formation; Limestone; Lower Permian; Magnesium; mantle; Mantle plumes; Maokou Formation; Mineral resources; Original Article; Oxygen isotopes; Paleozoic; Permian; petroleum; Petrology; Qixia Formation; Seawater; Sedimentary facies; sedimentary rocks; Shoals; solid Earth (tectonophysics); stratigraphic units; Stratigraphy; Strontium; Strontium isotopes; Yunnan China; China; Yunnan China; dolostone; East Yunnan; dolomitization; middle Permian; thermal convection; Emei mantle plume
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756820000503

Dolostones are widely developed in the middle Permian rocks of East Yunnan, China, mainly in the shoal-facies Maokou Formation. The previously reported dolostone formation mechanisms cannot explain the distribution and geochemical characteristics of these dolostones, in particular their strontium, magnesium and oxygen isotope signatures. To help predict the distribution of dolostone reservoirs and reduce the exploration risk and cost, this study proposes a new model of dolomitization: open thermal convection dolomitization. In this new dolomitization model, Mg2+ in dolomitizing fluids originates mostly from seawater, with a minor component coming from deep hydrothermal fluids. Elevated heat flux (in this case due to the nearby Emei mantle plume) causes spatial temperature variations in the fluid along the circulation flow pathways, resulting in fast and pervasive dolomitization of limestone. The proposed model not only explains the characteristics and distribution of dolostones in the study area but also serves as a reference for predicting the distribution of dolostones in other areas subjected to thermal convection.